Pre-filled syringes and auto-injectors are devices that are well known in the prior art for the delivery of liquids, often for the delivery of a liquid medicament to a patient. Both pre-filled syringes and auto-injectors tend to be constructed from a cylindrical barrel for containing the liquid with a plunger and needle to effect delivery of the liquid. The liquid is stored in the barrel and sealed at one end by the plunger and at the other by a cap. Sometimes such devices include a staked needle (i.e. a permanently fixed needle) which will have a cap over the needle to seal the device. The plunger is either depressed by the user to expel the liquid drug via the needle, or, in the case of auto-injectors, the plunger is depressed by an energy source which is often a compression spring.
These conventional devices suffer from many drawbacks including stability problems arising from the interaction of the medicament with the materials forming the device, such as the barrel glass, the plastic elastomeric plunger, the metallic needle, the adhesive used to stake the needle, and any necessary lubricants. The filling of these conventional devices is also problematic. The placement of a plunger during filling makes it difficult to fill many known devices bubble free and without risk of contamination. Movement of a plunger during storage due to expansion and contraction of air bubbles within the filled device may result in contamination of the drug.
Additionally the liquid medicament is sealed within the barrel by a moving plunger. It is, therefore, difficult to completely seal the medicament and keep it sterile while also allowing the plunger to be capable of movement.
Furthermore, the barrel is often made of brittle glass which is breakable both in use and during production and filling.
In most devices the liquid is in contact with the needle during storage. This can lead to problems such as blockages due to drug crystallization within the needle and medicament instability due to the interaction of the drug with the metals in the needle.
The filling procedures for conventional pre-filled syringes need to be complex to ensure sterility at all times.
It is an aim of the invention to provide a better injector.